1. Field of the Invention
The present invention relates to a turbocharger including a valve configured to open and close a circulation hole for an exhaust gas to or from a turbine housing.
2. Description of the Related Art
Turbochargers have been conventionally known in which a turbine shaft is rotatably supported by a bearing housing with a turbine impeller provided to one end of the turbine shaft, and with a compressor impeller provided to the other end of the turbine shaft. This turbocharger is connected to an engine. The turbine impeller is rotated by an exhaust gas discharged from the engine. The rotation of the turbine impeller is transmitted to the compressor impeller via the turbine shaft, and the compressor impeller is thus rotated. Thereby, the turbocharger compresses air with the rotation of the compressor impeller, and supercharges the engine with the compressed air.
A turbocharger described in Japanese Patent Application Laid-Open Publication No. H11-044219 (Patent Document 1) includes a wastegate valve. The wastegate valve allows part of an exhaust gas guided into a turbine housing to reach a downstream side of the turbine impeller by bypassing a turbine scroll passage which communicates with the turbine impeller. The wastegate valve is formed from: a stem pivotally supported by a bearing placed in the turbine housing; an attachment plate having an insertion hole into which the stem is to be inserted; and a valve body attached to the attachment plate.
Along with a turn of the stem, the wastegate valve is closed with a contact surface of a valve body coming into contact with a seat surface which is provided with the circulation hole of the bypass passage in the turbine housing. For this reason, if the contact surface of the valve body comes into contact with the seat surface in an inclined manner due to dimensional errors and the like, the valve cannot be closed completely. With this taken into consideration, the wastegate valve is designed to absorb the influence of the errors by providing a clearance between the valve and the attachment plate to provide the valve with a movable range in an inclination angle with respect to the attachment plate. To put it concretely, a projecting portion jutting out from an opposite side of the valve body from the contact surface is inserted through a through-hole provided in the attachment plate, and a part of the projecting portion which sticks out from the insertion hole is fixed by a nut with a clearance left between the valve body and the attachment plate. In this case, the inclination is made variable so that the contact surface of the valve body is located parallel to the seat surface even if the contact surface of the valve body comes into contact with the seat surface in an inclined manner.